1. Technical Field
This technology pertains generally to chip-to-chip communication, and more particularly to short-range chip-to-chip communication using differential current mode multiple-frequency modulation-demodulation.
2. Background Discussion
Conventional serial I/O is based on multiplexing and demultiplexing digital communications. To increase communications bandwidth using these conventional schemes, one first turns to increasing the clock rate. However, each process technology has its own limitations on clock rates, whereby one must often increase the number of I/O connections to increase the bandwidth, and as a result manufacturing costs increase. These costs are even further increased in 3D integrated circuit integration, such as those based on through-substrate-via (TSV) for vertical interconnections. The number of TSVs for the I/O is non-scalable due to fundamental physical or mechanical constraints. Higher than a certain number of TSVs per unit area (or population density) leads to thinned Si substrate (about 100 μm/tier) which can result in collapse. Therefore, this thinning can seriously limit inter-tier communication bandwidth in 3D integrated circuits.
Thus, chip-to-chip communication circuits with higher communication bandwidths have been sought which do not require concurrent increases in the clock rate or additional I/O connections. Traditional chip-to-chip communication connections rely on voltage signaling over interconnected metal wires. Even advanced approaches for communication between chips, such as multi-frequency-band quadrature amplitude modulation (QAM) circuits for chip-to-chip connections as taught by the inventors in the previous application (provides high bandwidths without increased clock rates or added I/O connections), includes the use of voltage signals with or without termination.
These existing methods for implementing multiband or QAM modulation and demodulation circuits are targeted for long distance communications. This is because the distance between communications is long and extensive power amplifiers and low noise amplifiers can be used for transmitting or receiving communication signals in voltage mode instead of in current mode.
Accordingly, the present technology provides enhanced chip-to-chip communications for short interchip distances of a few inches or less.